Centrifugal furnace for fusion and casting under vacuum



llg- 10, 1965 L. RlGATTl-LUCHINI 3,199,158

CENTRIFUGAL FURNACE FOR FUSION AND CASTING UNDER VACUUM Filed July 30, 1962 2 Sheets-Shel??l 1 0l l C@ 67 IH e1g -4 l @go 7 63 U O 7 69 4 Agen ,for Afp/ton Aug- 10, 1965 1 RIGATTl-LucHlNl 3,199,158

GENTRIFUGAL FURNACE FOR FUSION AND CASTING UNDER VACUUM Filed July 50, 1962 2 Sheets-51112151I 2 United States Patent O tij This invention relates to a centrifugal furnace for fusion and casting under vacuum, particularly of alloys for dental laboratories or goldsmith alloys.

The importance of the fusion under vacuum, as far as the quality of the molten product is concerned, is weLl known.

t has been found that the quality and the characteristics of the molten product considerably improve if, beside the fusion, also the casting, the hardening and the cooling occur under vacuum.

ln order to provide a device suitable to carry out the fusion, the casting and the hardening operations under a high vacuum, it was necessary to solve several diflicult technical problems.

lt is, in fact, the object of this invention to solve in an economically convenient manner the above-mentioned problems by means of a centrifugal furnace for fusion and casting under vacuum.

Another object of the invention is to provide a centrifugal furnace of the above-described type in which a number of operative stages of the furnace are carried out dur inn the rotation of the furnace.

Still another object of the invention is to provide an ecient furnace which will be economical, of low consumption and simple in operation and maintenance; which will be resistant to wear and of long life and which will have easy accessible and replaceable parts.

These and other objects which will become more apparent from the following description are attained by the centrifugal furnace for fusion and casting under vacuum according to this invention, characterized in that it comprises a chamber defined by a hermetically closable housing, in which there is contained at least one fusion crucible, communicating with at least one fusion mold within said chamber, as Well as rotary support means for said housing, heating means for said chamber, cooling means for said housing, means for imparting a rotation Vto said housing, means for cooling said housing While the same is rotating, and furnace actuating means` The invention will now be described with reference to a preferred embodiment illustrated, by way of a non restrictive example, in the accompanying drawing, in which:

FlG. l represents a perspective view of the external assembly of the furnace according to the preferred embodiment;

FIG. 2 represents a section along to the furnace mean plane, in which the rear part of the device has been omitted;

FIG. 3 represents the rear part of the device shown in FIG. 2;

FlG. 4 represents a top View of the furnace housing; and

FlG. 5 represents a sectioned view of the cover of the housing.

With reference to the accompanying drawing, the furnace is constituted of a box l, enclosing the supporting framework of the furnace. Within the box l there are arranged the various actuating and transmission groups of the apparatus according to the invention, The furnace proper comprises a cylinder 2 having a double walled skirt or jacket formed of an outer wall 3 and an inner wall 6l. The bottom of cylinder 2 is, in turn, constituted of a doud,l9,l58 Patented Aug. l0, 1965 ble wall with internal bottom Wall 5 and external bottom wall e, whilst the front portion can be closed by means of a cover 7 provided likewise with a double wall jacket S having a deflector Wall 8a (FIG. 5). The cover closes the cylinder 2 in a fluid-tight manner by means of the annular gasket 9 and its closing and opening movements are guided by a pair of pipes lll and ll engaging slidingly in sleeve supports l2, i3, ltand l2', i3', 14', respectively and provided at diametrally opposite sides of cover 7. Pipe lll communicates with the interspace provided by the jacket 8 of cover 7 and the same applies for pipe ll on the other side of the cover (FIGS. 1 and 4).

Pipe l@ is connected to a rubber hose l5 which is connected with its end to the fitting i6 communicating with the jacket 3, 4 of cylinder 2, whereas the end opposite to the end connected to cover 7 of pipe ll is connected to another rubber hose ld', leading to the discharge outlet. Jacket 5, 6 of the bottom of cylinder 2, communicating with jacket 3, Il, has a fitting i7 to which there is connected a llexible hose i8 leading to the cold water source which will be described below. Cover 7 has further closing clamps 19, 19 (FIG. l) hinged to supports 14 and 14', respectively, with screw locking means Ztl and 2%', respectively, which enable to tightly press cover 7 against cylinder 2, thus ensuring a duid-tight closing allowing the vacuum providing suction action.

The furnace proper comprises, further, an internal chamber 2l surrounded by an electrical heating resistance Z2 spiral-wound around chamber 2l and immersed in a suitable refractory material 23. The electrical resistance 22 is connected through the bolt 24 with the insulating electrical conductor 26, which is connected in turn with Contact terminals 27 (FIGS. l and 3) which will be described below. On the symmetrically opposite part there is provided an analogous non represented electrical connection, connecting the electrical resistance 22 with the other electrical pole 27. The bolt 24, consisting preferably of copper, passes through the fluid-tight metal sleeve 25 and the electrical insulation is obtained through the insulating plastic sheath 25a, which expands radially by screwing nut 24a, thus providing the necessary xing and sealing of the conductor bolt 2d.

lnside the chamber 2l there is arranged the graphite Crucible .'23 having a cylindrical vessel shape, which shows in the upper part an opening 29 for iilling with the material to be molten, said opening 29 being aligned with hole 3d provided in the refractory material and with hole 3l passing through the walls of cylinder 2, so as to enable to see through tne peep hole 32 the contents of Crucible 2S. inspection hole 32 is tted with a cover 33 having an inspection opening 34. In the furnace 3l there is provided a lens 35 which closes in a fluid-tight manner the inspection hole.

3e is a thermocouple indicating the temperature within the furnace, which is read on the scale 38 (FIG. l) connected to the therrnocouple through conductor 37. The fusion chamber 2l is surrounded by quartz layers 3@ and d@ which provide for the necessary electrical insulation. Crucible 7.3 lits within the cylindrical opening of fusion chamber 2l defined by the refractory material of the electric resistance and communicates through hole 4l with the cavity l2 defined by the discoid mold 43 supported on the bracket 144 fastened on the cover 7. The travel of the opening displacement of cover 7 is slightly greater than the thickness of the mold 43, whereby, in the opening position of the cover 7, the mold 42 can be easily taken off the furnace, the same removal possibility existing in connection with Crucible 28.

Housing 2 of the furnace is supported through brackets 45.1 and 45 (FlG. l) on the T-beam 45, the web i7 of which is hinged through bolt 48 on supporting half-rings 49 and 4a'v (PIG. 1) provided on both Sides of the web 4'7 and lxed on the rotating disc 5t) by means of lugs 51 t and 52 projecting from disc 5t? and wielded thereon. Lugs 51 and 52 are arranged between the half-rings 49 and 49 and the latter are ,fastened to the said lugs 51 and 52 by bolts 53 and 54, Bolt 4S permits rotation of the beam 46 through a small, angle, the limits of which being determined by the edges 55 and 56 of the projecting lugs Sl'and 52, respectively. Beam 46 can be locked in' one of its positions by means of the locking member 57 provided as a cam means and cooperating with acorresponding hole provided in the web 47 and not visible in the figure.

On the rear part of beam 46 there is provided a counterweight 58 sliding by way of sliding block over the beam 46 and showing a lock screw 53. Still on the rear part of beam 46 there are providedV the contact blades 27 for electrically connecting the furnace resistance with the electric source through counter terminals 59 supported on an axially sliding rod of). Still on the rear part of the beam 46 Vthere is mounted the connection piece 61 of the piping for the vacuum pump, which connection can be coupled with the connection 62 communicating with the vacuum pump, not visible in the figure. Connection 61 is provided with a side connection @30h which there is fastened a exible hose 64 (FIG. l), the -other end of which being connected to the connection 65 communicating with housing 2 and fusion chamber 2l. The

, connection 65 is branched laterally and shows on the upper part a vacuum meter ed toV control thefvacuum reached in the fusion chamber. :Near the connection 6l there is provided al valve 67 of any known type, which is either closed or opened depending on the position in which handlel 63 is turned. The handle 65 serves also tofasten connection Y61 on connection 62.

Rotating support disc t) carries a toothed rim 69 in mesh with pinion 7i) of an electric motor non represented in the drawing vand connected to shaft 71 extending vertically towards the aforesaid electric motor.` y

' Disc 50 is rigidly connected to the bush or rotating7 sleeve member 72 rotatable about its ,own axis through ball bearings 73, the fixed race ring of which is fastened on cylinder 74 rigidly connected to the support platform 75, which is a part of the framework of the apparatus according to this invention. Bush 72 is mounted on the bush V76 rotating on axial thrust ball bearings "I7V and on ball bearing 78, the fixed race ring of which is rigidly fitted on stationary tubular member or pipe 79. The ball bearing 77 rests on bottom 80, rigidly connected to the support housing 74 and showing a central hole through which there passes pipe 79 having Valateral branching 31 which is inclined thereto. `Bush 72 is covered' on the upper part with a disc-shaped cover member S2 having a central hole through which there passes the pipe section or tubular piece 83 having a diameter substantially equal to, and aligned with, pipe 79. Pipe ysection 83 showsan inclined branching 34 projecting as a bossV from the uppery plane of the disc member 82.

From the foregoing it can ybe seen that the furnace y proper, together with beam 46, half-rings 49 and 49'., support disc 50, disc member 82, bush 72 and bush 76 are turnable around the axis of the pipe '79 thanks to ball bearl place Vthe pipe 85 to which same is welded, providing forV the sealing between internal and external pipe 35 and 79 respectively. Y t

It is to be noted that pipes 79 and Y85 are xed. y

' Pipe 85 penetrates with its upper end within the pipe section 33 and is aligned with the internal pipe section or pipe piece 39 having a diameter substantially equal to the fixed internal pipe S5 and slightly spaced therefrom by a gap 90, which allows rotation of pipe S9 with respect to fixed pipe 85. Y

On the lower part of cap S6 there is provided a helical spring 9i which pushesV downwardly a bush 92 with ring gasket 93 and ring gasket 94, which gaskets actas a sealing means between the xed-pipe 79 and the rotating member 72. V'Such a packing between the rotating members can advantageously be of the Angst-Pster type.

Beneath the sleeve 72 there is provided a conical annularV defiector member 95 Vwhich is rigidly fastened on pipe 79 which drains Vthe water possibly leaking through the packings 92-94 towards the channel 96 provided in the wail of bush 7d through which channel said water is vdrained in the annular space between bush '76 and support Vadvantageously be acock of the water supply network,

passes through the xed internal pipe 8S into 4the rotating.

pipe section 39 and from this through the rubber hose 18,.

which is connected to pipe section 89, into the boss 17 whence cooling waterA passes into jackets 3-4 and 5 6 to reach then the boss iti, from which, through rubber hose 15, the water passes into pipe lib and from pipe Htl into jacket 8 of cover 7, passing then, guided by a specially provided annular deflector 8a, into pipe 1l, egressing then` therefrom through exible hose i6'V connected to the -end of pipe 11. v

, The other end of Yrubber hose 16 Vis2 connected to the projecting inclined branching .84 of pipe section 33, where by the liquid, which has already effected the cooling of the furnace, passes into the interspace between pipe V83 and pipe S5 and then into the interspace betweenpipe 79 and pipe 35 to subsequently go out discharged through pipe 3l.

It is to be noted that at the gap 9i) between pipe S5 and S9 there is no dispersion'of cold water current flowing upwardly due to the tendency of the iiuid'threads to direct ow upwardly without deviating. To this also contributesthe temperature differential of the water flowing in the pipe and the warmer water coming from pipe 84.

Such tendency to avoid mix-up is also confirmed by thewell-known fluid thread theory. Obviously, the interspace between pipe 79and the cavity in the bush V72 will be filled with water for the fluid-tight sealing of which will provide the above-named Angst-Pster-type packing, whilst on the upper part the water leakage will be prevented by the packing 99.y n, 'Y

The device according to the above-described embodiment is further provided with a controlling relay electrical circuit whichcan automatically control the various operations of the furnace. Y

v The operation of the apparatus is as follows:

Once the Crucible with material to be molten has been inserted together withsthe mold 43 into the furnace, and cover 7 has been closed, cylinder 2 is manually rotated until aligning connection ,61,with connection 62 and terminals 27 with counter-terminals S9, which, by actuationof a specially provided contact, are causedto raiserfor a givenlength. Cooling water circulation cock is then openedand by .actuating the handle of the cam means 57 the beam dris slightly rotated in vertical plane, whereby connection 61 joins connection 62m a Huid-tightV manner and terminalsjr27V are driven into terminals 59 which, in the` meantime, have raised in their upper end actuates the vacuum pump and switches on the Contact, supplying electrical energy to the heater resistance, which starts heating the fusion chamber of the furnace. The duration of the heating can be regulated by means of a specially provided heating time regulating device. Such heating time will be dependent upon the quantity of material used and nature of material involved.

Otherwise, the electrical energy supply to the heater can also be controlled by the temperature reached in the furnace, which temperature, through the thermocouple 36, causes the circuit to be broken once a predetermined temperature has been reached. Whilst heating is going on, cooling water circulation continues and the vacuum pump operates until reaching a determined vacuum pressure` Then begins the fusion stage which is started by means of a push-button of the controlling circuit. The various operations are actuated by an eccentric or camshaft driven by a special motor unit, which, whilst having initially brought terminals in their upper position, now cause terminals 59 with their axially sliding shaft 63 to gradually lower as the fusion phase starts. The heating terminates, when terminals S9 get detached from terminals 27 by the controlling device and at the same time the small motor, actuating the centrifugation of furnace 2 through shaft "il, pinion '7d and toothed wheel 69, is caused to operate.

Centrifugation is thus started, thanks to which the molten mass in the Crucible is launched in the cavity l2 of the mold through hole 4l and remains withheld in such cavity 42 during the entire rotation of the furnace until hardening of molten material in the cavity 42 is accomplished.

During centrifugation, cooling of the furnace by means of cooling water through the above-described circuit is continued. Upon completion of centrifugation and once material cast in the cavity 42 has been hardened, the rotation of the furnace is arrested and the valve 67 is opened, thereupon cover 7 is opened and mold 43 and Crucible 28 are taken off.

In such a way the fusion and casting operations are completed under vacuum and immediately after removal of the mold the furnace is ready for the subsequent fusion and casting operation.

Due to the fact that the furnace is cooled also during centrifugation, such furnace is ready for the subsequent operative cycle immediately after removal of the mold and Crucible from the preceding operation, so that it is possible to complete every fusion and casting cycle in about 5 minutes, thereby making the furnace productivity very high.

The rotating assembly weighs about kg. in this embodiment and counter-weight 58 is refulated in such a way as to conveniently equalize dynamical forces developed during the centrifugation in order to decrease stresses on supports and rotating shaft.

A preferred embodiment of the invention has now been described, it being understood that same can undergo several changes and modifications within the scope and spirit of the invention as dened by the following claims.

l claim:

. A centrifugal casting apparatus, comprising,

a stationary frame, a rotatable air tight electric furnace, bearing means for rotatably supporting said furnace on said frame and defining an axis of rotation of said furnace,

said bearing means including, a rotating sleeve member beneath said surface and in rigid rotatory relation therewith and coaxial with said axis of rotation, said sleeve member having an upper end and a lower end and defines an inner chamber,

a stationary tubular member coaxial with and projecting within said inner chamber through said lower end, the inner diameter of said rotating sleeve member being greater than the diameter of said stationary tubular member,

a stationary pipe within said stationary tubular member,

at said upper end of said sleeve member a tubular piece within and rigid with said rotating sleeve member, said tubular piece having a diameter greater than the diameter of said stationary pipe and being coaxial with and offset in the axial direction with respect to said stationary tubular member to provide a first gap between said stationary tubular member and said tubular piece,

within said tubular piece and peripherally spaced therefrom a pipe piece coaxial to and rigidly connected with said tubular piece, said pipe piece being coaxial with and offset in the axial direction with respect to said stationary pipe thereby providing a second gap therebetween offset with respect to said rst gap,

slidable packing means between said lower end of said rotating sleeve member and the outer periphery of said stationary tubular member,

a cover member closing the upper end of said rotating sleeve member, said cover member having a bore receiving said tubular piece and said pipe piece providing independent passages through said cover member,

said electric furnace having a heating chamber offset with respect to said axis of rotation, a resistor surrounding said heating chamber, a removable Crucible within said heating chamber, a removable mold within said furnace near said Crucible, duct means connecting the interior of said crucible with the interior of said mold, said mold being more distant from said axis of rotation than said heating chamber, a cooling jacket near the periphery of said furnace, an inlet opening for said cooling jacket and an outlet opening therefor,

first pipe means connecting said tubular piece with said inlet opening and second pipe means connecting said pipe piece with said outlet opening,

transmission means to transmit rotary motion to said furnace,

conductor means for detachably connecting said resistor with a current supply,

further duct and valve means to connect said heating chamber with a vacuum source,

and a cover to open and hermetically close said furnace.

2. A centrifugal casting apparatus according to claim l, wherein said tubular piece and said stationary pipe have equal diameters and wherein said pipe piece and said stationary pipe have equal diameters and wherein said second gap is within said tubular piece.

3. An apparatus according to claim 1, wherein said cover has a cover cooling jacket, at least two hollow rods fixed on said cover and communicating with said cover cooling jacket of said cover, sliding supports being provided on said furnace supporting said hollow rods and allowing longitudinal displacements thereof, flexible hoses being further provided connecting said hollow rods with the cooling jacket of the furnace, said cover cooling jacket having a deector member imparting a tortuous motion to the cooling liquid owing through said cover cooling jacket.

4. An apparatus according to claim l, wherein said bearing means further comprise a disc member rigid with said rotating sleeve member, said disc member having a toothed rim in mesh with said transmission means, two parallel laterally spaced half-rings fixed on said disc and extending in a plane perpendicular to said disc, a beam supporting said furnace at one end thereof and having a web portion extending between said half-rings, a hinge means hingedly connecting said web portion with said half-rings, stop means limiting the rotation of said web portion about said hinge means, controllable cam means preventing rotation ofssaid web portion, an adjustable counter-weight on said beam, and wherein said further duct and valve means include a valve on the other end of said beam, a rst connecting piece on said beam Vand communicating with said valve and a Vsecond connecting piece on said stationary frame communicating With the vacuum source, said rst and said second connecting pieces communicating with each other in one position of said beam.

Q 13 References Cited by the Examiner UNITED STATES PATENTS 1,767,023V 6/30 Thomas et a1. 22-65,1 5 2,637,079 5/53 Kemppe 22e-65.1 3,052,001 9/62 Brennan 22-65 MARCUS U. LYONS, Primary Examiner. MCHAEL V. BRNDISL Examiner. 

1. A CENTRIFUGAL CASTING APPARATUS, COMPRISING, A STATIONARY FRAME, A ROTATABLE AIR TIGHT ELECTRIC FURNACE, BEARING MEANS FOR ROTATABLY SUPPORTING SAID FURNACE ON SAID FRAME AND DEFININ AN AXIS OF ROTATION OF SAID FURNACE, SAID BEARING MEANS INCLUDING, A ROTATING SLEEVE MEMBER BENEATH SAID SURFACE AND IN RIGID ROTATORY RELATION THEREWITH AND COAXIAL WITH SAID AXIS OF ROTATION, SAID SLEEVE MEMBER HAVING AN UPPER END AND A LOWER END AND DEFINES AN INNER CHAMBER, A STATIONARY TUBULAR MEMBER COAXIAL WITH AND PROJECTING WITHIN SAID INNER CHAMBER THROUGH SAID LOWER END, THE INNER DIAMETER OF SAID ROTATING SLEEVE MEMBER BEING GREATER THAN THE DIAMETER OF SAID STATIONARY TUBULAR MEMBER, A STATIONARY PIPE WITHIN SAID STATIONARY TUBULAR MEMBER, AT SAID UPPER END OF SAID SLEEVE MEMBER A TUBULAR PIECE WITHIN AND RIGID WITH SAID ROTATING SLEEVE MEMBER, SAID TUBULAR PIECE HAVING A DIAMETER GREATER THAN THE DIAMETER OF SAID STATIONARY PIPE AND BEING COAXIAL WITH AND OFFSET IN THE AXIAL DIRECTION WITH RESPECT TO SAID STATIONARY TUBULAR MEMBER TO PROVIDE A FIRST GAP BETWEEN SAID STATIONARY TUBULAR MEMBER AND SAID TUBULAR PIECE, WITHIN SAID TUBULAR PIECE AND PERIPHERALL SPACE THEREFROM A PIPE PIECE COAXIAL TO AND RIGIDLY CONNECTED WITH SAID TUBULAR PIECE, SAID PIPE PIECE BEING COAXIAL WITH AND OFFSET IN THE AXIAL DIRECTION WITH RESPECT TO SAID STATIONARY PIPE THEREBY PROVIDING A SECOND GAP THEREBETWEEN OFFSET WITH RESPECT TO SAID FIRST GAP, SLIDABLE PACKING MEANS BETWEEN SAID LOWER END OF SAID ROTATING SLEEVE MEMBER AND THE OUTER PERIPHERY OF SAID STATIONARY TUBULAR MEMBER, A COVER MEMBER CLOSING THE UPPER END OF SAID ROTATING SLEEVE MEMBER, SAID COVER MEMBER HAVING A BORE RECEIVING SAID TUBULAR PIECE AND SAID PIPE PIECE PROVIDING INDEPENDENT PASSAGES THROUGH SAID COVER MEMBER, 